Technical Abstract:
Failure to remove sugarcane post-harvest residue often reduces ratoon crop yields in temperate climates. A series of experiments was conducted to determine the effects of various residue management practices on sugarcane yield. For the first experiment, timing of post-harvest residue was based on the following physiological stages: pre-dormancy, complete dormancy, intermediate dormancy, and post-dormancy. Removal methods consisted of partial removal from the row top by mechanical means, complete removal by burning, and no removal. Residue removal treatments were performed on first, second and third ratoons grown on both clay and silt loam soils. Sugar yields following burning at pre-dormancy (6800 kg ha-1), complete dormancy (6610 kg ha-1), and mechanical removal at pre-dormancy (6500 kg ha-1) were greater than the control (6190 kg ha-1). Ratoons responded similarly to the residue management practices evaluated, and effects were consistent on both clay and silt loam soils. The second experiment investigated the compounded stresses of post-harvest residue retention and residual glyphosate effects in ratoon crops (following a ripener application the previous year). Where ripener was applied, post-harvest residue retention lowered sugar yields by 21% (3150 kg ha-1) compared to plots where the residue was not removed. On the other hand, where ripener was not used, post-harvest residue retention lowered sugar yields by 6% (920 kg ha-1) compared to plots where the residue was removed. For the third experiment, increasing nitrogen rates by 22 and 44 kg ha-1 compared to the traditional nitrogen rate of 130 kg ha-1 applied during normal fertilization practices in mid-spring was investigated as a potential practice to mitigate the yield loss associated with residue retention. This additional nitrogen did aid in achieving yields similar to burning with the standard 130 kg ha-1 rate of nitrogen, but due to the high price of nitrogen this is not an economically feasible option. For the fourth experiment, we evaluated a modified hay bailer that removed the majority of the residue off of the top 0.8 meter of a 1.8-meter row; traditional mechanical options reposition residue from the row top to the wheel furrow. The bailer’s gathering device running at the soil surface appeared to mechanically disrupt underground stubble, and yields were less than when residue was removed by burning. To ensure optimum yields of subsequent ratoon crops, residue generated during the green-cane harvesting of sugarcane in temperate climates should be removed from harvested fields as soon after harvest as possible, especially if ripener was applied the previous season. Finding an economically feasible alternative to burning continues to be a research challenge. We are currently investigating new removal techniques that are more effective in incorporating residue into the soil than currently available methods. USDA scientists are also screening all commercial varieties, advanced lines, and basic germplasm for tolerance to these post-harvest residue blankets.